Reverse phase connective tissue repair composition

ABSTRACT

A biocompatible connective tissue repair composition which comprises a therapeutic material and a carrier comprising a means for achieving reverse phase characteristics, and methods for using said composition. The therapeutic material can be demineralized bone powder, and the carrier can be a poloxamer such as poloxamer 407.

This is a continuation of U.S. application Ser. No. 08/922,068, filedSep. 2, 1997, now U.S. Pat. No. 6,3 09,659.

FIELD OF THE INVENTION

This invention concerns prosthetic materials. More particularly, itconcerns a biocompatible material that exhibits reverse phase behavior.

BACKGROUND ART

Osteogenic bone repair materials are known in the art. These materialscontain an osteogenic material, such as demineralized bone powder in acarrier, such as glycerol. See, e.g., U.S. Pat. No. 5,290,558, issuedMar. 1, 1994 to O'Leary et al., and U.S. Pat. No. 5,284,655, issued Feb.8, 1994 to Bogdansky et al.

The carrier of the bone material in the art is a liquid, having aviscosity generally somewhere between runny and paste-like. “Runny” bonerepair compositions have the advantage of being relatively easy to applyto and fill a bone defect, however they are disadvantageous in that thematerial also tends to readily flow from the defect site. Conversely,bone repair compositions with a “paste-like” consistency are harder toapply to a defect, yet tend to remain positioned at the defect onceapplied. Additionally, when any of the bone repair compositions in theart are placed in vivo and become warmed, they become even less viscous;the decrease in viscosity is due to the addition of thermal energy tothe composition.

Accordingly, there is a need for a bone repair composition that is easyto apply to a defect site, and which remains positioned at the site onceplaced at the site.

DISCLOSURE OF THE INVENTION

Disclosed is a biocompatible composition to facilitate repair ofconnective tissues. The composition can comprise demineralized bonepowder, and, a carrier comprising a means for achieving reverse phasethermodynamic characteristics when mixed with the bone powder. Thecomposition can be substantially liquid at 0° C., and substantially moreviscous at 35° C., such that the composition has a consistency like thatof paste floor wax or like solid shoe wax. The means for achievingreverse phase characteristics can comprise a block copolymer, such as apoly(oxyalkylene) block copolymer, which can be apoly(oxyethylene)-poly(oxypropylene)-poly(oxyethylene) triblockcopolymer. The triblock copolymer can be a compound of the formula:

The means for achieving reverse phase characteristics comprises apoloxamer, such as poloxamer 407. The block copolymer can be a soliddispersed in a biocompatible solvent such as sterile water.

Preferably, the carrier comprises a carrier of 25 weight percent of ablock copolymer dispersed in 75 weight percent of a biocompatiblesolvent. To vary the consistency of the composition, the weightpercentage of demineralized bone powder or other solid can be variedrelative to the weight percentage of the carrier in the composition. Forexample, a paste-like form of the composition comprises 50 weightpercent of bone powder and 50 weight percent of a carrier. A gel-likeembodiment of the composition comprises 30 weight percent of bone powderand 70 weight percent of a carrier.

The bone powder of the composition can comprise particles with a medianlength to a median thickness ratio of about 1.742:1, a mean length of0.25-1 mm (250-1,000 microns), and a mean thickness of about 0.5 mm (500microns).

Also disclosed is a method to facilitate the development of bone tissue,said method comprising: providing a biocompatible connective tissuerepair composition comprising demineralized bone powder, and, a carriercomprising a means for achieving reverse phase thermodynamiccharacteristics when mixed with the bone powder; and, placing thecomposition in a bony defect of a mammal. A prosthetic object can alsobe placed in the bony defect. The method can also comprise coating aportion of the prosthetic object with the biocompatible composition, andin this embodiment the step of placing the composition and the step ofplacing a prosthetic object can be contemporaneous.

MODES FOR CARRYING OUT INVENTION Definitions

By “reverse phase” or “reverse thermal behavior” is intended a materialthat exhibits a physical property of becoming more viscous or solidifiedupon addition of thermal energy. It is believed that the solidificationoccurs by a mechanism other than that due to evaporation andcorresponding loss of liquid.

As used herein, “ambient temperature” is 25° C., plus or minus 5° C.

As used herein, “body temperature” is 37° C., plus or minus 5° C.

As used herein, a “bony defect” or “bone defect site” is bonyenvironment of a mammal which comprises some viable bone tissue. Thedefect can be congenital, caused by trauma, or caused by disease.

“Osteoinductive” materials cause undifferentiated cells to differentiateinto a committed bone cell lines.

“Osteoinductive” materials provide support for cells of a bone celllineage, e.g., permitting cells of a bone cell lineage to grow along orthrough a matrix or lattice.

Preferred Modes

In a preferred embodiment, the composition of the present invention is aflowable liquid when applied to a bony defect, whereupon the compositionbecomes increasingly solidified or viscous as it warms to ambient and isfurther solidified as it warms to body temperature. Upon being warmed tobody temperature, a preferred composition of the invention is a solid orhighly viscous fluid. The reverse phase compositions in accordance withthe invention are significantly different in principle from bone repairmaterials in the art, and do not function in the same way.

The composition comprises a therapeutic material for treating one ormore connective tissues; and, a carrier. The therapeutic material can bea material to facilitate repair of connective tissues, i.e., a“connective tissue repair material.” The carrier achieves reverse phasecharacteristics when mixed with the therapeutic material.

The therapeutic material can be a material that is osteoinductive,osteoconductive, or a material that is osteoinductive andosteoconductive. The therapeutic material can be xenogeneic, allogeneic,or autogenic. The therapeutic material can be alloplastic. Asappreciated by one of ordinary skill in the art, the therapeuticmaterial can comprise combinations of various therapeutic materials.

Examples of osteoinductive material include but are not limited to bonepowder (mineralized or demineralized), tissue growth factor beta (TGF-β)types 1 through 13, bone morphogenetic protein (BMP) types 1 through 15,or combinations thereof.

Examples of therapeutic materials that are osteoconductive include butare not limited to xenogeneic bone (mineralized or demineralized); thexenogeneic bone can also be subjected to deproteination. Presentlypreferred xenogeneic source are porcine and bovine.

Therapeutic materials that are osteoinductive and osteoconductiveinclude particulate human allograft, e.g., of demineralized bone.

Examples of alloplastic materials comprise gypsum, corallinehydroxyapatite, synthetic hydroxyapatite, calcium carbonate, calciumphosphate, calcium sulfate, biodegradable polymeric materials, orcombinations thereof.

A presently preferred composition comprises demineralized osteogenicbone powder in a carrier; the composition can be applied to a bonedefect site to induce new bone growth. This composition of the presentinvention comprises demineralized bone particles or granules (referredto herein as “demineralized bone powder”) in an inert biocompatiblecarrier.

In a preferred embodiment, the particles/granules have a median lengthto median thickness ratio about 1.742:1, a mean length of 0.25-1 mm(250-1,000 microns) and a mean thickness of about 0.5 mm (500 microns).

The presently preferred biocompatible carrier of the composition of theinvention is a material that confers reverse phase thermodynamicproperties on the composition. The use of PLURONIC® F127 as a componentof an osteointegration promoting composition is set forth in U.S. Pat.No. 5,503,558, issued Apr. 2, 1996 to the inventor herein, Cameron C. L.Clokie; and in PCT International Publication No. WO 95/13099. In apresently preferred embodiment, the carrier comprises a polymer marketedby BASF (Parsipanny, N.J.) as PLURONIC® F127. PLURONIC® F127 is apoly(oxyalkylene) block copolymer; more specifically, apoly(oxyethylene)-poly(oxypropylene)-poly(oxyethylene) poly(oxyethylene)triblock copolymer; it is a member of a class of compounds calledpoloxamers. (Schmolka, “A Review of Block Polymer Surfactants” J. Am.Oil Chemists Soc. 54:110-116 (1977)). Several members of the poloxamerfamily exhibit reverse phase thermodynamic characteristics. PLURONIC®F127 is also known by the name “poloxamer 407.” (Schmolka, “A Comparisonof Block Polymer Surfactant Gels” J. Am. Oil Chemist Soc. 68:206-209(1991)). PLURONIC® F127 has an average molecular weight of approximately12,500. (Schmolka, “A Comparison of Block Polymer Surfactant Gels” J.Am. Oil Chemist Soc. 68:206 -209 (1991)) The structure of the PLURONIC®F127 polymer is depicted as follows:

In preferred embodiments of a composition of the present invention, thecarrier is a liquid diluted in a solvent or is a solid dispersed in asolvent. In one embodiment, PLURONIC® F127 is dispersed in a solventsuch as sterile water. The PLURONIC® F127 carrier is vastly different insize, molecular weight, and chemical structure than carriers in the art.The carrier is also substantially different in terms of its functionalproperties than any carrier of a bone repair material in the art.

The proposed composition has a unique physical property, being flowableat refrigerated temperatures and increasingly solidified at elevatedtemperatures, such as ambient and body temperatures. This property isreferred to in the art as “reverse phase” or “reverse thermal behavior”.Due to the reverse phase property of the proposed composition, thecomposition is generally manufactured at refrigerated temperatures, suchas 5° C. Manufacturing is done at refrigerated temperatures to enhancemixing of the components of the composition, since the proposedcomposition comprising an aqueous suspension of PLURONIC® F127 begins tobecome more viscous at ambient temperature, and is increasingly viscousand solidified at body temperature. Generally, a composition of theinvention will be twice as viscous at 35° C. as it is at 0° C.

For example, the preferred PLURONIC® F127 carrier in the composition ofthe present invention (when dispersed in an appropriate amount ofsterile water), has the unique property of being a liquid atrefrigerated temperature and increasingly solidified, then solid atelevated temperature, absent the effects of evaporation and concomitantloss of water. This property is called “reverse phase” or “reversethermal behavior” because it is the exact opposite of the thermodynamicproperties exhibited by standard carriers.

It is believed that the reverse phase property is due, at least in part,to the fact that PLURONIC® F127 is composed of discrete blocks of bothhydrophilic (i.e., oxyethylene) and hydrophobic (i.e., oxypropylene)subunits. (See e.g., Schmolka, “A Comparison of Block Polymer SurfactantGels” J. Am. Oil Chemist Soc. 68:206-209 (1991)).

In contrast, standard carriers, as well as all liquids, manifest thetypical physical property of becoming increasingly flowable uponaddition of thermal energy, such as occurs when the liquid is heated tobody temperature. However, the preferred carrier in a composition of thepresent invention becomes less flowable as energy is added to it eitherby heating or by shaking.

The unique reverse phase thermodynamic properties of the composition ofthe present invention allow the product to function in a substantiallydifferent, and preferred manner relative to other flowable bone repairproducts. When applied to a bone defect site, the reverse phase propertyof the preferred carrier provides support characteristics for thecomposition which are substantially different than the characteristicsof standard carriers. Enhanced support is provided by the composition ofthe invention. The preferred PLURONIC® F127 carrier of the compositionof the present invention helps to provide support characteristics whichare unlike those of any standard carrier. This is because thecomposition is flowable at refrigerated temperature and can thus readilybe applied to a bony defect site, but it becomes increasingly viscousand solidified once it is warmed at the site. The solidification of thecomposition of the present invention achieves several beneficialeffects. When solidified, the composition does not flow away from thedefect site, and the solidified product immediately augments andfacilitates structural support at the defect. Also, since the osteogeniccomposition of the invention is initially liquid, it readily fills adefect, then becomes solidified and achieves enhanced osteogenesis.Moreover, with preferred compositions of the invention, comprising asterile aqueous colloidal suspension of PLURONIC® F127 as a carrier anddemineralized bone powder, the carrier will resorb or dissolve afterabout three days, leaving the osteogenic bone powder at the bone defectsite. It is believed to be advantageous that the carrier disperses asthis then allows enhanced ingrowth of connective or vascular tissues.

In a composition of the invention, the weight percentages of thetherapeutic material and the carrier can each be varied. For example,the weight percent of the therapeutic material can vary between about 20to 80 weight percent of the composition, and the weight percent of thecarrier can vary between about 20 to 80 weight percent of thecomposition. Furthermore one or more additional components can bepresent in a composition of the invention, such as antibiotics,analgesic, anti-inflammatory agents, or agents to promote development ofconnective or circulatory system tissues.

EXAMPLES Example 1

To obtain a composition having a gel-like consistency, the compositioncomprised 70 weight percent of a colloidal suspension of PLURONIC® F127and 30 weight percent of bone powder. In this example, the carriercomprised 25 weight percent of PLURONIC® F127 powder dispersed in 75weight percent sterile water.

A composition of the invention is available as DynaGraft™ Gel (GenSciRegeneration Laboratories, Inc., Irvine, Calif.); this product is acomposition comprising demineralized allograft bone from a single donormixed with an inert preservative and a biocompatible carrier. Thecomposition has a “gel” consistency and is provided in a sterile, singlepatient use package.

The tissues used in the bone repair composition are recovered by UnitedStates tissue banks, from carefully screened donors, according tostandards established by the American Association of Tissue Banks. Allsuch tissues meet stringent specifications during donor screening andlaboratory testing in order to reduce the risk of transmitting anyinfectious disease.

For example, each donor is tested and found to be negative for (at aminimum): hepatitis B surface antigen, human immunodeficiency virus 1and 2 antibodies, HTLV-1 antibody, hepatitis C virus antibody, andsyphilis. The tests were performed by a CLIA approved laboratoryutilizing FDA-licensed test kits. The medical and social history of thedonor revealed no risk factors for, or clinical evidence of, HIV orhepatitis infection.

This biocompatible composition in accordance with the invention wasproduced under environmentally controlled conditions using stringentcleaning, preservation, and sterilization procedures. All steps arerigorously quality controlled in accordance with accepted methodologiesin the art.

DynaGraft™ Gel is indicated for use in surgical procedures in whichosteogenesis, calcification or bony fusion is needed to achieve orenhance the quality of the final result. Accordingly, DynaGraft™ Gel canbe used in a variety of orthopedic, reconstructive, and dental bonegrafting procedures. DynaGraft™ Gel may be used alone as a bone graft incases in which the graft is not intended to provide weight bearingsupport or dimensional integrity to the graft site. If the graft isintended to be weight bearing, the composition should be used withappropriate fixation. DynaGraft™ Gel can, therefore, be used as acomplement to musculoskeletal implants such as joint replacementprostheses, intraoral implants, and internal and external fixationdevices for procedures in which demineralized freeze-dried boneallograft would be used.

The composition is sterilized by a targeted 2.5 megarads of electronbeam irradiation as terminal sterilization. When implanting thecomposition, sterile technique should be maintained to minimize the riskof post-operative complications. Use of the composition iscontraindicated when there is active or latent infection at or near thesurgical site.

The composition should be stored long-term in a clean, dry place at roomtemperature. It should be kept out of direct sunlight and should not befrozen. DynaGraft™ Gel does not require rehydration prior to use.

The packaging of all DynaGraft™ implant compositions has been speciallydesigned to provide ease of use within the surgical field. For example,the composition can be packaged within syringes that are kept sterilewithin one or more foil containers. DynaGraft™ Gel is supplied in 1.0cc, 5 cc, and 10 cc syringes.

To use the composition packaged in syringes within foil containers, thepackaging is opened by peeling open the outer foil and, using steriletechnique, transferring the entire inner package to the sterile field.The inner package is then opened and the syringe removed. Immediatelybefore use, a protective cap which covers the tip of the syringe isremoved. The composition is then extruded by pushing on the syringeplunger to deliver the desired volume. Appropriate placement and/orfixation are critical factors in the avoidance of potentially adverseeffect on product service life.

Accordingly, the DynaGraft™ Gel is bacteriologically sterile during thestated shelf life in an unopened and undamaged package. The product mustbe used before the expiration date. Unused product should be properlydiscarded.

Example 2

To obtain a composition having a paste-like consistency, the compositioncomprised 50 weight percent of a colloidal suspension of PLURONIC® F127and 50 weight percent of bone powder. In this example, the carriercomprised 25 weight percent of PLURONIC® F127 powder dispersed in 75weight percent sterile water.

A composition of the invention is available as DynaGraft™ Putty (GenSciRegeneration Laboratories, Inc., Irvine, Calif.); this product is acomposition comprising demineralized allograft bone from a single donormixed with an inert preservative and a biocompatible carrier. Thecomposition has a “putty-like” consistency and is provided in a sterile,single patient use package.

The tissues used in the bone repair composition are recovered by UnitedStates tissue banks, from carefully screened donors, according tostandards established by the American Association of Tissue Banks. Allsuch tissues meet stringent specifications during donor screening andlaboratory testing in order to reduce the risk of transmitting anyinfectious disease.

For example, each donor is tested and found to be negative for (at aminimum): hepatitis B surface antigen, human immunodeficiency virus 1and 2 antibodies, HTLV-1 antibody, hepatitis C virus antibody, andsyphilis. The tests were performed by a CLIA approved laboratoryutilizing FDA-licensed test kits. The medical and social history of thedonor revealed no risk factors for, or clinical evidence of, HIV orhepatitis infection.

This biocompatible composition in accordance with the invention wasproduced under environmentally controlled conditions using stringentcleaning, preservation, and sterilization procedures. All steps arerigorously quality controlled in accordance with accepted methodologiesin the art.

DynaGraft™ Putty is indicated for use in surgical procedures in whichosteogenesis, calcification or bony fusion is needed to achieve orenhance the quality of the final result. Accordingly, DynaGraft™ Puttycan be used in a variety of orthopedic, reconstructive, and dental bonegrafting procedures. DynaGraft™ Putty may be used alone as a bone graftin cases in which the graft is not intended to provide weight bearingsupport or dimensional integrity to the graft site. If the graft isintended to be weight bearing, the composition should be used withappropriate fixation. DynaGraft™ Putty can, therefore, be used as acomplement to musculoskeletal implants such as joint replacementprostheses, intraoral implants, and internal and external fixationdevices for procedures in which demineralized freeze-dried boneallograft would be used.

The composition is sterilized by a targeted 2.5 megarads of electronbeam irradiation as terminal sterilization. When implanting thecomposition, sterile technique should be maintained to minimize the riskof post-operative complications. Use of the composition iscontraindicated when there is active or latent infection at or near thesurgical site.

The composition should be stored long-term in a clean, dry place at roomtemperature. It should be kept out of direct sunlight and should not befrozen. DynaGraft™ Putty does not require rehydration prior to use.

The packaging of all DynaGraft™ implant compositions has been speciallydesigned to provide ease of use within the surgical field. For example,the composition can be packaged within jars that are kept sterile withinone or more foil containers. DynaGraft™ Putty Gel is supplied in 2.5 cc,5-cc, and 10 cc jars.

To use the composition packaged in jars within foil containers, thepackaging is opened by peeling open the outer foil and, using steriletechnique, transferring the entire inner package to the sterile field.The inner package is then opened and the jar and a spatula are removed.The jar lid is opened in a sterile manner and composition putty isremoved with the spatula or other hand-held instrument.

Appropriate placement of the composition and/or fixation are criticalfactors in the avoidance of potentially adverse effects on productservice life.

Accordingly, the DynaGraft™ Putty is bacteriologically sterile duringthe stated shelf life in an unopened and undamaged package. The productmust be used before the expiration date. Unused product should beproperly discarded.

CLOSING

It must be noted that as used herein and in the appended claims, thesingular forms “a,” “and,” and “the” include plural referents unless thecontext clearly dictates otherwise. Thus, for example, reference to “aformulation” includes mixtures of different formulations and referenceto “the method of treatment” includes reference to equivalent steps andmethods known to those skilled in the art, and so forth.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although any methods andmaterials similar to or equivalent to those described herein can be usedin the practice or testing of the invention, the preferred methods andmaterials are now described. All publications mentioned herein are fullyincorporated herein by reference.

What is claimed is:
 1. A biocompatible connective tissue repaircomposition, comprising: (a) demineralized bone powder, and (b) amixture of a poly(oxyalkylene) block copolymer and water that exhibitsreverse phase behavior when its temperature is increased from ambient tobody temperature.
 2. The composition of claim 1, wherein thepoly(oxyalkylene) block copolymer is PLURONIC™ F127.
 3. The compositionof claim 1, wherein the mixture of poly(oxyalkylene) block copolymer andwater is 25 percent weight poly(oxyalkylene) block copolymer and 75percent weight water.
 4. The composition of claim 1, wherein thecomposition is 30 percent weight demineralized bone powder and 70percent weight poly(oxyalkylene) block copolymer and water.
 5. Thecomposition of claim 1, wherein the composition is 50 percent weightdemineralized bone powder and 50 percent weight poly(oxyalkylene) blockcopolymer and water.
 6. The composition of claim 1, wherein thedemineralized bone powder is xenogeneic, allogeneic or autogenic.
 7. Thecomposition of claim 1, wherein the demineralized bone powder isxenogenic and from a porcine or bovine source.
 8. A method to facilitatethe development of bone tissue comprising: placing a biocompatibleconnective tissue repair composition at a bone defect site, wherein thebiocompatible connective tissue repair composition comprises: (a)demineralized bone powder, and (b) a mixture of a poly(oxyalkylene)block copolymer and water that exhibits reverse phase behavior when itstemperature is increased from ambient to body temperature.